1. Field of the Invention
The present invention relates to a light source controller and an image display device that include solid-state light sources.
2. Description of the Related Art
Conventionally, there has been known an image display device including a solid-state light source such as a light emitting diode (LED) or a laser diode (LD), and an optical modulator that modulates light emitted by the solid-state light source (for example, Japanese Patent Application Laid-open Publication NO. 2006-18196). In the image display device, the solid-state light source generates heat when power is supplied to the solid-state light source. When the environmental temperature of the solid-state light source increases, the light amount emitted by the solid-state light source decreases.
Note that another image display device provided with a cooling device for cooling a solid-state light source has been also proposed for the purpose of reducing a decrease of the light amount, the decrease caused due to heat generated by the solid-state light source (for example, Japanese Patent Application Laid-open Publication NO. 2004-144794 (claim 1, paragraphs [0036] and [0037], FIG. 3)).
Here, by taking an LED (light-emitting diode) light source as example, it is known that a drive current-light amount property varies in proportion to a change of the environmental temperature of the LED light source.
For example, as shown in FIG. 3, a red LED has a property (also called an over-roll below) in which the outgoing light amount increases up to a certain level in proportion to an increase of the drive current, while the outgoing light amount conversely decreases beyond the certain level of the drive current. Moreover, the red LED has a property in which the higher the environmental temperature becomes, the more largely the outgoing light amount decreases even when the same drive current is applied to the red LED. Here, for example, in FIG. 3, T1 denotes a room temperature (for example, 20° C.), T2 denotes a steady temperature at a time when the light source is lighting, and T3 denotes a temperature higher than the steady temperature. In short, the relationship among the environmental temperatures is T1<T2<<T3.
In general, a drive current supplied to a solid-state light source is controlled by a certain step width (ΔC). Specifically, when the light amount emitted by a solid-state light source is short, the drive current is increased by a certain step width, and then a determination is made as to whether or not the light amount emitted by the solid-state light source reaches a target light amount. The drive current is controlled by repeating such processing so that the light amount emitter by the solid-state light source would reach a certain light amount (the target light amount).
However, in the case of the conventional technique, the light amount emitted by a solid-state light source fails to quickly reach the target light amount in some cases, since the drive current is controlled by the certain step wide. In other words, it is difficult to determine the increasing amount of drive current so that the light amount emitted by the solid-state light source reaches the target light amount, since the drive current-light amount properties are influenced by the environmental temperature of the solid-state light source as shown in FIG. 3.